Supercharging of Internal Combustion Engines: One of the long-term goals of the automotive manufacturers is to reduce fuel consumption and emissions of modern automotive vehicles powered by internal combustion engines (ICE) while increasing engine efficiency. One approach to reaching this goal is reducing the ICE displacement. However, downsized engines having reduced swept volume typically exhibit insufficient power and torque when operating with normal aspiration. Performance of downsized engines may be recovered by supercharging. It is well known in the art that ICE power output increases with increased weight of air ingested into engine cylinders and available for combustion. Weight of intake air ingested into engine cylinders can be increased by either (1) increasing the pressure of intake air beyond what can be accomplished by natural aspiration or by (2) reducing the temperature of intake air or by (3) a combination of (1) and (2). A supercharged ICE, therefore, receives combustion air with higher density than a naturally aspirated ICE. As a result, supercharging allows generating increased power from an engine of a given displacement or, generating a given power output from an engine of smaller size, weight, cost, and emissions. In addition, reduced charge temperature is known to reduce ICE emissions by decreasing charge pre-ignition also known as knocking.
One commonly used type of a supercharger is the exhaust-gas turbocharger which typically includes a turbine and a centrifugal compressor on a common shaft. The turbine is rotated by exhaust gases from the engine and spins the compressor. The compressor receives intake air, compresses it, and supplies it to ICE combustion chamber(s). Turbochargers provide the advantages of relatively smooth transition from natural aspiration to supercharged operation while utilizing some of the residual energy of hot exhaust gas, which would otherwise be largely wasted. The compression of intake air increases its temperature and thus undesirably limits its density. The challenges of constructing a turbocharged ICE include: 1) reducing as much as possible the response time lag and 2) reducing the temperature of air delivered to ICE. Information relevant to attempts to overcome these challenges and the disadvantages of such attempts are described below.
A turbocharged ICE is susceptible to a slow response time known as the “turbo lag” which is caused by the low pressure and low quantity of exhaust gases that are available to operate the turbine at low engine speeds. This translates to insufficient quantity of intake air delivered to the engine and results in insufficient torque at low engine speeds. The turbo-lag problem may be corrected in-part by the use of a variable nozzle turbine, which alters the cross-sectional area through which the exhaust gas flows in accordance with engine speed. However, this approach provides only a partial solution, adds complexity and cost, and reduces reliability. Another approach to reducing the turbo lag may use one or more jets of air injected onto the compressor wheel of a turbocharger as disclosed, for example, by Williams et al. in U.S. Pat. No. 3,190,068. Such air jets may be directed generally onto the vanes of the compressor wheel so as to transfer a part of their momentum to the wheel and thus accelerate the rotational speed of the compressor. Air injected in this manner becomes a part of the intake air ingested by the engine.
Recently, an electrically-assisted turbocharger (also known as the “e-turbo”) has been proposed to remedy the turbo lag. Since the e-turbo makes supercharging independent of engine speed, it promises to virtually eliminate the turbo lag. Generally, in the e-turbo, electric power drawn from vehicle electric system (e.g., battery) is provided to an electric motor which spins a turbo-compressor. There are two different types of e-turbo known. The first type is formed by directly coupling an electric motor to the shaft of a conventional exhaust turbocharger, as disclosed, for example, by Kawamura in U.S. Pat. No. 4,958,497. A drawback of this approach is that during acceleration of the e-turbo to operational speed the electric motor has to overcome the compound inertia of both the turbo-compressor and the exhaust turbine while additionally being exposed to very high temperatures. The second type of e-turbo is formed by coupling an electric motor to a turbocompressor, as disclosed, for example, by Woolenberger et al., in U.S. Pat. No. 6,079,211. This type of an e-turbo can be used in series or in parallel with a conventional turbocharger to reduce the turbocharging lag and to increase torque at low ICE speeds, such as disclosed, for example, by Hoecker et al., in U.S. Pat. No. 6,889,503. However, both e-turbo approaches face the challenge of attaining the extremely fast startup and acceleration to reach operating speeds of 50,000 to 70,000 revolutions per minute (rpm) in less than one second. To meet this challenge may require ultrahigh power electronics and electric power source combined with sophisticated computer control. In particular, according to an article authored by Thomas Kattwinkel et al. entitled “Mechatronic Solution for Electronic Turbocharger” SAE paper number 2003-01-0712 published by the Society of Automotive Engineers, Inc., Warrendale, Pa., the e-turbo electric demand may not be satisfactorily met with the standard 12 volt automotive battery system.
In summary, prior art does not teach a supercharged ICE system that is effective during the conditions of high torque and low engine speed, has a fast response, is simple, economical, and can be easily retrofitted onto existing ICE, does not require exotic electric motors and power supply, avoids exposing electrical components to high temperatures, and reduces susceptibility to charge pre-ignition. Furthermore, the prior art does not teach an ICE where intake air is mixed with cold air from a turboexpander. Moreover, prior art does not teach an ICE supercharged by an a turbocompressor operated by a turboexpander expanding high-pressure air, wherein compressed intake air produced by the turbocompressor is cooled by the cold air produced by the turboexpander. It is against this background that the significant improvements and advancements of the present invention have taken place.